1. Field of the Invention:
The present invention relates to a recyclable vehicular cushioning material and seat.
2. Description of the Prior Art:
Among the known vehicular cushioning materials is polyurethane. Polyurethane is in general use as a vehicular cushioning material because of its good durability, cushioning properties, and processability as well as its low price. However, polyurethane has a disadvantage of being combustible. Upon combustion, it gives off a large amount of toxic gases, which endanger passengers in the case of vehicular fire. To cope with this situation, polyurethane is incorporated with a halogen-containing flame retardant. This flame retardant, however, does not make polyurethane incombustible completely but gives off a large amount of toxic halogen gas once combustion starts. This is quite dangerous particularly in the case of fire in a tunnel or underpass.
Another disadvantage of polyurethane is that it becomes greatly deteriorated after use for a long period of time, and deteriorated polyurethane is usually disposed of because its reuse involves difficulties and a practical method for its recycling is still in the stage of investigation. The disposition of polyurethane is usually by incineration after collection by junk dealers. Outdoor incineration brings about air pollution with toxic gases (such as cyan gas). Incineration by an incinerator can remove toxic gases, but it is expensive because the incinerator is subject to corrosion by toxic gases. Therefore, polyurethane is usually disposed of by dumping in the site of land reclamation. Being a cellular material, polyurethane keeps the ground unstable. For this reason, a large amount of polyurethane is now left in an open space, and a very little of it is recycled at the present time.
Recently, a new vehicular cushioning material has appeared which is made with fibers to eliminate the stuffiness of seats. It is used for some deluxe cars. The fibers are natural fiber or synthetic fiber combined with an adhesive (such as polyurethane and rubber latex) for improved durability. It is anticipated that this cushioning material will follow the fate of polyurethane on account of its unique composition. Another new cushioning material is for the breathable seat designed to eliminate stuffiness. It is composed of three-dimensionally crimped thick polyester fibers bonded together with rubber latex. This cushioning material, too, will follow the fate of polyurethane because of its unique composition. Moreover, it involves a risk of candle effect (i.e. burning like candle) in the case of fire.
There is known a polyester fiber-based cushioning material in which three-dimensionally crimped polyester fibers are heat-bonded with low-melting non-elastomer copolyester fibers. This cushioning material has found use for mattresses because of its good moisture permeability (which alleviates stuffiness). Being thermoplastic, it may be regenerated by melting into fibers. Alternatively, it may be recovered in the form of monomer after methanolysis. Despite these advantages, it is not suitable for vehicular seats to be used under severe conditions because it is poor in permanent set resistance at high temperatures. In other words, it readily undergoes plastic deformation upon compression at 70.degree. C. because the bonding material is amorphous and it also greatly undergoes plastic deformation because its body material is polyester fiber made by a conventional method and having a glass transition temperature lower than 70.degree. C.
The covering of vehicular seats is usually made of nylon tricot, nylon moquette, polyvinyl chloride, and urethane-impregnated synthetic leather, which are superior in durability. The nylon covering is mostly disposed of together with the pad by incineration or land reclamation because its separation from the pad costs too much and it is difficult to collect it in such large quantities as to warrant the cost for recycling. (Nylon 6 can be recovered in the form of lactum after depolymerization and hence nylon fishing nets are collected for recovery.) Moreover, the covering for vehicular seats usually contains a halogen-based flame retardant so that it meets the requirements for flame retardance. Therefore, the covering of nylon, polyvinyl chloride, or polyurethane gives off a large amount of toxic cyan gas and halogen gas upon combustion, and these combustion gases are extremely dangerous in the case of vehicular fire. Their disposition by incineration is expensive if an adequate measure is to be taken to prevent air pollution. Therefore, they are often left or buried. The covering of polyester is supposed to be treated in the same manner as mentioned above if it is combined with a cushioning material of polyurethane or rubber.
Nothing has so far been proposed for the vehicular seat and its cushioning material having little stuffiness which are designed with safety and recyclability in mind.